A study of the aging mechanisms underlying sex and race differentials in longevity is proposed. In this study, the nature of aging mechanisms will be investigated in four longitudinal study populations, using methods expressly designed for the analysis of aging changes in longitudinal studies. These methods will describe the aging trajectories of both the study populations and individuals, in a variety of variables previously identified as relevant to aging processes, as well as age changes in the force of mortality as related to the aging mechanisms. In addition, these methods were designed to eal with a number of methodological and statistical issues that arise in the analysis of longitudinal data. Specific goals in the research plan will be: to assess comparability of measurements between different studies and analyse aging mechanisms and aging changes in mortality in each study; to examine information on aging changes in each study to determine their implications for observed mortality patterns in national population data. This study will primarily involve the disciplines of demography, psychology and gerontology. The work will involve a number of health-related issues such as the basis for sex and race differentials in longevity, the trajectory of aging changes and the implications of those processes for the resultant age structure of the elderly population.